Either direct dyes or oxidation dyes are generally used for dyeing keratinic fibers. Although intense coloring with good fastness properties may be achieved with oxidation dyes, the development of the color generally takes place under the influence of oxidizing agents such as H2O2, which in some cases may result in damage to the fiber. In addition, some oxidation dye precursors or certain mixtures of oxidation dye precursors may have a sensitizing effect in persons with sensitive skin. Direct dyes are applied under milder conditions. However, they have the disadvantage that the colorings have insufficient fastness properties, in particular during washing of the hair, but also with respect to external influences such as sunlight or reactive environmental chemicals, for example swimming pool water. Such colorings are also generally much more sensitive to shampooing than the oxidative colorings, so that an often undesirable change in shade, or even a visible discoloration, then occurs much more quickly.
In addition to an attractive hair color, the consumer also desires lustrous hair. Lustrous hair looks attractive and healthy, and the hairstyle is perceived as being well cared for and full of vitality. In many cases, the consumer has a number of wishes that he/she would like to fulfill at the same time; i.e., the consumer wants an attractive hair color, and also wants lustrous hair. For practical reasons, for this purpose the consumer would prefer to use only one treatment method on the hair.
Various methods are already known from the prior art for coloring the hair in a great variety of shades. A large number of various formulations is disclosed in CA 2613049 A1, for example. However, there is still a need for novel coloring agents which produce intense coloring, and at the same time, exceptionally high luster.
In particular, there is a need for novel coloring agents which are able to produce a long-lasting luster. The hair which is dyed with these agents should not lose its luster after one, or at the most, several, weeks, and instead, its luster should still be noticeable even after multiple hair washings.